Rheostat



June 13, 1933. i N. c. SCHELLENGER v 1,913,686v

RHEOSTAT Filed Jan. 31, 1930 g Fig] F 3/ .33 0 37 4 g 32 g 36 5/ k 46//7) ll'i v J [72 v-en for Newton Cfic/ZcZlerzyer M an};

Patented June 13, 1933 UNITED STATES PATENT. OFFICE NEWTON G.SCHELLENGER, OF'ELKHART, INDIANA, ASSIGNOR 'I'O CHICAGO TELEPHONE SUPPLY00;, OF ELKHAR'I', INDIANA,

A CORPORATION OF I INDIANA Application filed January 31, 1930. Serial1%. 424,775.

This invention relates to electrical rheostats and has for its principalobject the production of a new and improved rheostat that can be cheaplymanufactured without sacrificing quality of workmanship and materialsand this is a continuation in part of my application granted September15, 1931, No. 1,823,472.

r Electrical rheostats such as are used in radio sets, and other similarapparatus frequently' comprise a metallic shell containing a centrallylocated threadedbushing which serves as a bearing for the shaftof therheostat and also as. a mounting means for attaching the rheostat to asuitable panel or other supporting framework. Rheostats of this type areof very sturc construction and when securel mounted can givesatisfactory service over a long period of time without attention.

In my present invention I have provided a new and improved rheostat ofthis type, the improvement not only making the manufacture of therheostat a less costly operation but also making the finished product amore sturdv andtreliablerheostat than has been available heretofore.Rheostats built in accordance with the teachings of my n1- vention arecomnact in size and of simple design so that they may be mounted in asmall and somewhat inaccessible place and successfully operated sincethey require a minimum of attention.

Now to acquaint those skilled in the art with the teachings of myinvention, reference is madeto the accompanyin drawing in which apreferred embodiment of it is shown by way of example and in which:

Figure 1 is a vertical section taken through a completely assembled andmounted rheostat;

Figure 2 is an end view-of the-rheostat shown in Figure 1;

Figure 3 is a detail view of one of the terminals of the rheostat;

Figure 4 is a plan view of the end of the resistant element and theterminalattached to it;

Figure 5 IS a cross-sectional view of Fig.'

vsulating strip 21.

are 4, taken along the line 5-5 looking in the direction of the arrow;

Figure 6 is a fra mentary view ofthe planar portion of the shell,showing the serrated hole therein; and

Figure. 7 is a fragmentary view taken along. the line 7-7 of Fi ure 2showing the details of the terminal portion of the shell.

The rheostat comprises a cup-like metallic shell 1, which is preferablymade of sheet brass or other non-magnetic material and formed in theshape of a cup by a punchpress operation. The circular central portion2, of the shell forms a mounting plate and the flange 3, is formedintegral with this central portion 2, and disposed around its peripheryat right angles to its plane. Centrally located in the planar portion 2,is a serrated hole 4, through which the bushing 5, is projected with theshoulder 6, disinto the serrations in the perforation 4,

thereby securing the bushing against rotation with respect to the shell.

The bushing 5, is also provided with a threaded portion 8, adapted toreceive a mounting nut 9 which mounts the rheostat on a suitable panel10. Prefer-ably a washer 11, is interposed between thenut, 9 and thepanel although this may be omitted if desired.

The resistance. element of the rheostat comprises wire 20 space woundupon an' in- The insulating strip is of generally rectangularcross-section with its edges chamfered as at 22, to slightly round themso that the wire can be against the strip without necessitating itsbeing bent at a sharp angle. The wire is laid in grooves 23, which arecut in the end of the strip between the chamfered corners 22. Thegrooves partly encircling the wire hold it rigidly in place space it sothat adjacent convolutions of the winding do not touch each other.Preferably the chamfers are cut at an angle of on the strip and closelylaid approximately to the side of the strip, although an arcuate chamfermay be substituted. The strip 21 is preferably made of a moistureproofed insulating material such as treated fiber or a phenolcondensation product.

Near the ends of the strip 21, are circular perforations 24 and 25through which the prongs 26 and 27 of the'term'inal 28 are projected.These prongs are formed as integral projections of the body of theterminal and are pushed through the openings 24 and 25 and betweenadjacent convolutions of the wire 20 on the strip, the projecting endsthen being bent over and pressed down firmly against the wire 20 tosecurely hold the terminal on the strip and to also hold the wire endsecurely thereon. This clamping of the end of the wire 2O secures a goodelectrical contact between the wire and the terminal 28 as well assecurely holding the wire on the strip 21.

An insulating washer 30 is disposed against the planar portion 2 of theshell and an insulating strip 31 is disposed against the inside surfaceof the flange 3 and against the washer 30. The washer 30 and the strip31 may be a moisture proofed fiber or a phenol condensation productorany' other preferred insulating material. Theinsulating strip 31 islonger than the inside periphery of the flange 3 so that its ends areoverlapped as shown at 32 Figure 2, and these overlapped ends aresubsequently perforated to receive a rivet for holding the parts in theframe. The resistance element 29 is disposed inside the cup against thewasher 30 and strip.

The resistance element 29 is placed in the shell 1 with the ends 36 ofthe strip 21 butting against each other so that the hoop strength of thestrip holds it and the in: sulator 31 in the shell. Terminals 28 arelocated on the outside surface of the element adjacent the insulator 31.

After the element 29 has been placed in place in the shell 1, the flange3 of that shell is shrunk by a punch-press-operation to reduce theperimeter of the shell and thereby cause it to exert a radial force onthe element; 29 to securely bind the element against the inside surfaceof the flange by its own hoop strength, which resists the tendency ofthis radial force to reduce its circumference. This shrinking alsocreases the flange 3 as shown at 38 Figure 1, said crease tendin' tostiffen the flange to thereby enable it to securely hold the resistanceelement under compression and in place against it. v

The dies employed in the shell shrinking operation are provided withslots which permit leaving the portions 28 of the shell behind theterfninals 28, undisturbed so that two socket like outwardly extendingprojections are left in the finished shell. The terminals 28 andinsulator 31 liein these projections, the walls of which prevent turningof the terminals and thereby enhance the mechanical strength of therheostat: This shrinking of the shell binds the resistance element 29 sotightly in place that an element cannot warp even though the insulatingstrip on which its is wound absorbs a considerable amount of moisture.This arrangement and the use of a moisture proof material in theconstruction of the strip insures that the rheostat will remain in goodoperating condition over a long period of time without attention.

The central terminal 33 is fitted on the inside of the element 29, andinsulated therefrom by an insulating washer 34 which may be made of anypreferred moisture proof insulating material. The terminal 33 is longenough to span over the contacts 23 at the ends of the resistanceelement, and is held in place by a rivet or eyelet projecting through ahole 35 in the terminal 33 and through the abutting ends 36 of theinsulating strip 21 on which the element 29 is wound. The rivet 37 alsoextends through overlapped ends 32 of the insulator 31 and through theflange 3 of the shell 1, to securely bind the resistance element, theinsulating washer, and the terminal in place in the shell.

To establish a connection with the resistance element 29, I provide acontactor 40 which is riveted to the end .of the shaft 41 which projectsthrough an opening in the bushing 5 and terminates in a larger diameterportion 42 on which is located a knob or other suitable handle 43 foradjusting the rheostat. The shoulder 44 formed between the large andsmall portions of the shaft 41 fits against the threaded end 8 of thebushing 5, and a spring washer 45 may be interposed between the shoulderand end of the bushing to keep the shaft tightly in place in thebushing.

The contactor 40 is provided with a serrated or hexagonal-shaped openingthrough which the end of the shaft 41 is projected and then riveted overas shown at 46, the riveting operation swedging the end of the shaftinto the serrations in the contactor 40 to securely lock the contactoron the shaft against rotation with respect to it. The inside end of thebushing 5 is countersunk as at 47 to prevent the shaft from bindingshould the shaft be enlarged slightly at its extreme end portion duringthe riveting op eration.

The spring arms 48 of the cont-actor 40 terminate in a contact member49which is formed on a radius so that it will slit e over the wire-t2O onthe element 29 without cut ting into or displacing that wire on theelement. These spring arms are spaced outwardly from the base portion ofthe contactor by means of an integral offset connecting portion, whichserves as a spacing member between the arms and the portion of thecontactor which is secured to the shaft. This forms a contaetor havingits base portion and its spring arms lying in substantially parallelspacedplanes, with the base portion being disposed within the confinesof the resistance element. tacting portion 49, of the cont-actor 40 isformed at an angle of approximately (35 degrees to the side of theelement so that it engages the element 49 tangentially to the chanifer22 011 the corner of the strip ll. By this arrangement,-the point ofcontact between the contacting arm and the wire is immediately adjacentto the cross grooves 23 in the strip, so that the side thrust placed onthe wire by the movement of the, contactor 40 will not displace thewires on the strip. Moreover the co-ntactor 49 does not bear on the wireover the slots 23 so that there is no likelihood of the contactor ridingon the extreme edge of the insulating strip 21 rather than on the wireif the wire is extremely small and quite completely embedded in theslots 23.

The bending of the contacting arm 49 permits establishing a good contactwith the resistance element 29 without projecting the end of the arm 49beyond the outside edge of the element 29. In fact the extreme endportion of the contactor 49 falls of the outside edge of the element 29an:l therefore is spaced a considerable distance. away from theinsulating strip 31 and the flange 30f the shell, both of which projectbeyond the free edge of the resistance element 29.

Preferably the fi nge 3 of the shell is cut away asat 50 so that whenthe terminals 2 and 33 are bent outward they fall in a plane adjacentthe plane containing the edge of the flange 3 so that the open or backface of the rheostat is perfectly flat and all moving and currentcarrying parts are/within that space so that the rheostat-"may bemounted in close proximity to other equipment.

The contact 33 is provided with a pair of projecting bosses 51 which liein the path of the contacting arm 49 and limit its rotation to an arc ofslightly less than 36!) degrees. The. projections 51 are so positionedthat the contactor 49 engages the end turns of the winding 29 that areshort-circuited by the terminal clips 26 and 27 so that the rheostatnever open-circuits and a smooth take-off is assured when the contactor49 is moved away from the stops 51.

The rheostat so constructed is compact and can be cheaply manufacturedwithout sacrificing workmanship or material. Since the edge of theflange 3 projects beyond the free end of the resistance element 29, therheostat is well ableto withstand the more or less rough handling towhich it is sub- The con 'ing the rough handling a little short.

jected on the assembly line of a manufacturing plant, without damagingthe resistance element 29. This is particularly advam tageous if thewire 20 on the element is as small as two or three thousandths of aninch in diameter, as I have found that a majority of the open-circuitedrheostats are opened because the wires are nicked or broken durto whichthe. rheostat is subjected when it is being assembled in the electricaldevice in which it is used.

\Vhile I have chosen to disclosemy invention by illustrating a preferredeinbodiment of it, I have done so by way of example only as there aremany modifications and adaptations which ran be made by one skilled inthe art without departing from the scope and teachings of the.invention.

Having thus complied with the statutes and shown and described apreferred embodiment of my invention, what I consider new and desire tohave protected by Letters Patent is pointed out in the appended claims.

\Vhat is claimed is:

1. In a rheostat, an insulating winding strip' having a generallyrectangular crossseetion and having a pair of perforations near each ofits ends, a resistance wire wound on said strip, apair of terminals, anda pair of prongs on each terminal projected between the turns of saidwire and through said'perforations and clinched on the opposite side ofthe strip to bind the terminal on the stripand to establish anelectrical contact between the terminal and wire. I

2. In a rheostat, a moisture proof insulating strip having a pluralityof perforations near each of its ends, a resistance wire wound on saidstrip and over said perforations with its adjacent convolutions spacedapart, and terminals clinched on said strip and over said winding byprongs projecting through said perforations and around said wire.

3. In a rheostat, a moisture proof insulating strip having a pluralityof perforations near each of its ends, a resistance wire wound on saidstrip and over said perforations with its adjacent convolutions spacedapart, a pair of terminals, and a plurality of prongs on each terminalwhich are projected through said perforations to bind the terminal onthe strip and to establish electrical connection with the windin 4 4. Ina rheostat, a moisture proof insulating strip having a plurality ofperforations near each of its ends, a resistance wire wound on saidstrip and over said perfora- 5. An electrical rheostat comprisin a frameconsisting of a metallic disc having a flange disposed normally aroundits outer circumference, an insulating Washer dis posed against saiddisc, an insulating meinber disposed against said flange with its endsoverlapping, a resistance element disposed within said frame and againstsaid washer and insulating member, and having its ends abutting againstthe overlapped portion of said insulating member, the upper edge of saidelement falling short of the upper edge of said flange and insulatingmember, said elements being held in compression by said flange to bindsaid elements thereagainst, and a contactor having an arm which engagesthe edge of said element but falls short of said insulating member.

6. An electrical rheostat comprising a cuplike shell, an insulating discdisposed inside the planar portion of said shell, an insulating stripdisposed inside said shell, said strip being longer than theinsideperimeter of the shell and having its ends overlapping, a resistanceelement disposed against said disc and strip with its ends abutting overthe lapped portion of said strip, said shell being placed in tensionagainst said element to cause the hoop strength of the element incompression to bind the element, the strip and the disc in the shell, aclamping plate fitted inside said element but insulated therefrom, andmeans extending through said plate, the abutted ends of said element,the lapped portion of said strip and said shell for holding said platein said shell 7. An electrical rheostat comprising a frame consisting ofa metallic disc having a flange disposed normally around its outercircumference, an insulating washer disposed against said disc, aninsulating strip disposed around said flange against said washer andhaving its ends overlapping, a resistance element disposed within saidframe against said washer and insulating member, terminals on saidelement disposed between it and said insulating member, said elementbeing longer than the inside perimeteu of said member and being disposedunder compression with its ends abutting to hold it, the terminals, themembers and washer in said frame, and a third terminal for said rheostatdisposed inside said element but insulated therefrom and connected tosaid frame.

8. An electrical rheostat comprising a.

member, terminals on said element disposed between it and saidinsulating member, said element being longerthan the inside perimeter ofsaid member and being disposed under compression with its ends abuttingto hold it, the terminals, the member and washer in said frame, a thirdterminal for said rheostat disposed inside said element but insulatedtherefrom and connected to said frame, a contactor pivotall Y connectedat the'center of said disc and engaging said arm, and a pair of stopscarried by said third terminal for limiting the movement of saidcontactor about its pivot.

9. A contactor for a rheostat comprising a shaft, a base attached at oneof its ends to the end of said shaft and projecting to one side of it,an integ 'al offset spacing portion, a pair of integral arms projectingfrom the free end of said spacing portion outwardly of the end of saidshaft, and a contact member in which said arms verge.

10. A rheostat comprising a metallic cup, a resistance element disposedwithin said cup and insulated from it, a shaft pivotally supported inthe center of said cup, a contactor attached to said shaft, saidcontactor including a member engaging said element and a pair of arms oflength greater than the radius of said cup and verging in said member,said arms spaced outwardly of and normal to said shaft.

11. A rheostat comprising a cylindrical metallic cup, a pair of bossesprojecting radially from said cup, a resistance element disposed in andinsulated from said cup, terminals on said element disposed in andinsulated from said bosses, said element being compressed in said cup tohold itself and said terminals in place, and a third terminal disposedagainst the inside surface of said element but insulated therefrom andconnected to said shell.

12. A contactor for a rheostat comprising a shaft, a contactor baseattached to said shaft, a pair of arms spaced outwardly from andsubstantially parallel to said base, and a contact member into whichsaid arms converge.

13. A contactor for a rheostat comprising a shaft, a contactor baseattached to said shaft, a pair of arms spaced outwardly from andsubstantially parallel to said base, an offset spacing portion formedintegral with said arms and extending between said base and said arms,and a contact member into which said arms converge.

14. A contactor for a rheostat comprising a shaft, a contactor baseattached to said shaft, a pair of arms spaced outwardly from andsubstantially parallel to said base, an offset spacing portion formedintegral with and connecting said base and said arms, and an arcuatelycurved contact member into which said arms converge, said contact memherbeing angled with respect to the plane of said arms. I

15. In a rheostat, a shell, a resistance element disposed in said shelland insulated

